<< [a0 a1 ... ap] i any put >> << [a0 a1 ... ap] multi-index any put >> << s i any put >> integer i; string s; array of integers multi-index; The operator put <<any>> at the place i. Example: /a [1 2 3] def a 2 (Hi) put a :: --->[1 2 (Hi)] Example: /a [[1 2] [3 4]] def a [0 1] 10 put a :: ---> [[1 10] [3 4]]